This invention relates to an air cooled refractory covered injection lance for introducing reactive gases, such as halogen gases, below the surface of a molten metal bath to remove hydrogen contained within the molten metal bath.
Many methods for hydrogen degassification of steel are known and used in modern metallurgical operations. Vacuum degassing is one such method of molten steel degassification but this method requires large capital investments for the vacuum degassing facilities. A second method of degassification is the slow cooling of steel products such as blooms and slabs, to allow the hydrogen to diffuse naturally. However, such slow cooling extends processing time, ties up inventory and requires extreme care to ensure reliable results.
It has been discovered, as further described in co-pending U.S. Patent application Ser. No. 276,094 filed Nov. 23, 1988, U.S. Pat. No. 4,869,749 , that rapid removal of hydrogen from molten steel can be achieved by injecting a reactive halogen containing gas, such as tetrafluoromethane or dichlorodifluoromethane or sulfur hexafluoride fluoride, below the surface of a molten steel bath through an air cooled refractory coated lance. The injected halogen containing gas combines with the hydrogen within the molten steel bath and forms a compound which readily escapes from the molten steel at atmospheric pressures. However, it has also been discovered that halogen containing gases are prone to premature thermal decomposition when subjected to extreme high temperatures in the injection lance. It has been found that unless the injection lance components which come into contact with the halogen containing gases are maintained at a relatively cool temperature, the halogen containing gases within the lance will decompose into elemental fluorine and/or chlorine which corrodes and causes premature failure of the injection lance.